Die for press-molding optical elements and methods of manufacturing and using the same

Abstract: A die for press-molding glass optical elements which can press-mold glass optical elements having high melting points and various shapes repeatedly, which includes a base material (13) having high strength on which a cutting layer (12) having heat resistance and free cutting machinability is formed. After cutting the cutting layer (12) into the desired shape with high accuracy, the die is coated with a surface protective film (11). The cutting layer (12) is formed by an amorphous film or an alloy film containing one of P,B,Cu or Si. The surface protective layer (11) is formed by an alloy film comprising at least one of Pt,Pd,Ir,Rh, Os,Ru,Re,W,Ta. The cutting layer (12) can be formed by plating, evaporation, sputtering or ion plating the said film on the base material (13).

Description: This invention relates to a die used for press-molding glass optical elements having high surface accuracy. This invention also relates to the use of the die for the press-molding process, and to a method of manufacturing the die. In order to press-mold glass optical elements having high accuracy repeatedly by means of a die, it is necessary to use a die material which is stable at high temperatures, has excellent resistance to oxidation, and is inert with respect to glass. In addition, the material must have excellent mechanical strength so that the surface accuracy is maintained when pressed. On the other hand, the material must have excellent machinability so as to be machined precisely and easily. It is disclosed that die materials which meet these requirements to some degree are a mixed material consisting of titanium carbide (TiC) and metal (Japanese patent application No. JP-A-59121126) or a material comprising a base material of cemented carbide on which a precious metal film is formed (Japanese patent application No. JP-A-62096331). However, the conventional materials of the die do not meet the above-mentioned requirements completely. For example, the material of the die using a mixed material of TiC and metal has excellent mechanical strength, but is poor in machinability due to its extreme hardness. Thus, it is difficult to machine with high accuracy. In addition, this material has a further defect in that it easily reacts to lead (Pb) or an alkaline element contained in glass optical elements . When a material comprises a base material of cemented carbide on which a precious metal film is formed, a diamond wheel is used to machine the cemented carbide. At this time, it is difficult to form a fine shape due to wear of the diamond wheel. Therefore, a special processing device is needed. Furthermore, there are problems that the process take a long time and that the die is extremely expensive. A further problem is that a diamond tool used for cutting the hard base material is worn down during the process. Therefore, it is impossible to proceed with the cutting, and a shape having a small radius of curvature which can not be attained by a grinding process can not be fabricated. The following method of manufacturing a die has proposed a solution to the above-noted problems (Japanese patent application No. JP-A-62003031). A base material used here has excellent heat resistance, heat shock resistance, and strength at high temperatures. A fine cutting layer comprising a material which can be ground and cut excellently and is chemically stable and having a high melting point, for example, Pt-alloy film, is formed on the base material. After this layer is formed into a desired surface through a fine machining process, the mold surface is coated with a Pt-alloy film for protection. Another method of manufacturing a die is disclosed in JP-A-3023230 (which corresponds to EP-A-0404481). In this instance, a film formed on a base material of cemented carbide has good adhesion to the base material. On top of this, an electroless Ni-P plated film, for example, is formed as a fine cutting layer. After this layer is cut precisely into a desired surface, the mold surface is coated with an alloy film for protection. Accordingly, this document discloses a die and a method of manufacturing a die according to the preamble of claims 1 and 3 of the present application. However, using the above-noted manufacturing methods, the film formed as a cutting layer did not have sufficient strength so that the die was deformed when press-molded. Therefore, it was actually impossible to mold at high temperatures of 650°C and higher. It is an object of this invention to solve the above-noted problems by providing a die for press-molding glass optical elements having high melting points and various shapes repeatedly. This was not possible with conventional grinding methods. In order to accomplish these and other objects and advantages, a die for press-molding glass optical elements in the invention comprises a base material having heat resistance and sufficient strength to withstand the press-molding process of glass optical elements, and a cutting layer formed on said base material comprising a first alloy film comprising phosphorus (P) or a first alloy film containing boron (B). The cutting layer is covered with a second alloy film which includes at least one metal selected from the group consisting of Pt, palladium (Pd), iridium (Ir), rhodium (Rh), osmium (Os), ruthenium (Ru), rhenium (Re), tungsten (W), and tantalum (Ta). The first alloy film also contains one metal selected from the group consisting of Ni, Co, and Fe, and further contains one metal selected from the group consisting of Si, titanium (Ti), Cu, zirconium (Zr), niobium (Nb), molybdenum (Mo), Ru, Rh, Pd, hafnium (Hf), Ta, W, Re, Os, and Ir. It is preferable in this embodiment that an intermediate layer comprising at least one film selected from the group consisting of metal, carbide, nitrogen, and oxide is present between the base material and the cutting layer. The method of manufacturing a die for press-molding in a second embodiment of this invention comprises forming a base material having heat resistance and sufficient strength to withstand the press-molding process of glass optical elements into a shape similar to a desired shape of the die, forming a cutting layer on said base material comprising a first alloy film comprising P or a first alloy film containing B by means of at least one method selected from the group consisting of a plating method, an evaporation method, a sputtering method, and an ion plating method, and covering the cutting layer with a second alloy film which includes at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W, and Ta. The first alloy film further comprises one metal selected from the group consisting of Ni, Co, and Fe, and one metal selected from the group consisting of Si, Ti, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, and Ir. It is preferable that this embodiment further comprises forming an intermediate layer comprising at least one film selected from the group consisting of metal, carbide, nitrogen, and oxide between the base material and the cutting layer by means of at least one method selected from the group consisting of a plating method, an evaporation method, a sputtering method, an ion plating method, and a chemical vapor deposition (CVD) method. The use of the die of claim 1 or 2 in a method of press-molding glass optical elements according to a third embodiment of the invention comprises press-molding at a temperature of 650°C and higher. A die used for press-molding glass optical elements comprises a base material having heat resistance and sufficient strength to withstand the press-molding process of glass optical elements, a cutting layer on said base material comprising a first alloy film containing P or a first alloy film containing B, wherein the cutting layer is covered with a second alloy film which includes at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W, and Ta. The first alloy film containing P or B also comprises a metal selected from the group consisting of Ni, Co, and Fe, and further comprises a metal selected from the group consisting of Si, Ti, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, and Ir. In particular, the die according to the present invention comprises a base material having heat resistance and sufficient strength to withstand a press-molding process for optical glass, and a cutting layer formed on said base material comprising a ternary alloy film consisting of one metal selected from the group consisting of Ni, Co, and Fe, one metal selected from the group consisting of Si, Ti, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, and Ir, and one element selected from the group consisting of P and B. After this cutting layer is cut with high surface accuracy, an alloy film containing at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W, and Ta is formed as a protective film on the cutting layer. In this way, a die is provided which can be used to press-mold glass optical elements having high melting points and various shapes. By press-molding an optical glass at a press-molding temperature of 650°C and higher repeatedly, a large quantity of glass optical elements having high melting points and various shapes at a low cost can be produced which was impossible using conventional methods. Furthermore, by forming an intermediate layer between the base material and the cutting layer comprising at least one film made from a material selected from the group consisting of metal, carbide, nitrogen, and oxide, it is possible to prevent the cutting layer from peeling, and it improves the durability of the die. A die for press-molding glass optical elements which is manufactured according to the above-noted method, has sufficient strength to withstand the press-molding process by using a base material having excellent heat resistance and strength. This invention enables the die to be cut into a desired shape easily with high accuracy by forming a cutting layer which comprises a ternary alloy film comprising a metal selected from the group consisting of Ni, Co, and Fe, one metal selected from the group consisting of Si, Ti, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, and Ir, and one element selected from the group consisting of P and B. In addition, this die also attains the heat resistance and the strength at high temperatures which can stand the press-molding process of glass being press-molded at a temperature of 650 °C and higher. The die also prevents itself from welding with the glass by forming an alloy film containing at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W, and Ta as a surface protective film. As a result, this invention enables production of a press-molding die for glass having a high melting point and various shapes. By press-molding the glass using the die of this invention, it enables production of a large quantity of glass optical elements having high melting points and various shapes at a low cost which was impossible by the conventional grinding process. Furthermore, by forming an intermediate layer comprising at least one film made of a material selected from the group consisting of metal, carbide, nitrogen, and oxide, the adhesive strength between the base material and the cutting layer improves, and this prevents the film from peeling. Thus, it enables improved durability of the die. FIG. 1 is a cross-sectional view of one embodiment of this invention showing a die for press-molding glass optical elements. FIG. 2 is an outline view of a press-molding machine used in one embodiment of this invention. FIG. 3 is a cross-sectional view of one embodiment of this invention showing a die for press-molding glass optical elements. FIG. 4 is a cross-sectional view of one embodiment of this invention showing a die for press-molding glass optical elements. FIG. 5 is a cross-sectional view of one embodiment of this invention showing a die for press-molding glass optical elements. FIG. 6 is a cross-sectional view of one embodiment of this invention showing a die for press-molding glass optical elements. FIG. 7 is a cross-sectional view of one embodiment of this invention showing a press-molding die for glass optical elements. This invention is specifically described by referring to the following illustrative examples and attached figures. Example 1 A molding die of this embodiment is shown in FIG. 1. As shown in FIG. 1, the molding die of this embodiment comprises a base material of cemented carbide 13 on top of which a cutting layer 12 is formed into a desired shape with high accuracy. Furthermore, a Pt-Ir alloy protective layer 11 is formed on cutting layer 12 for protection. A manufacturing method of the molding die shown in FIG. 1 is described as follows. First of all, base material of cemented carbide 13 is processed into the shape similar to the desired shape by means of electrical discharge machining. Then, cutting layer 12 is formed by a sputtering method on top of the base material 13 which is roughly processed by the electrical discharge machining. After that, the cutting layer 12 is cut using a diamond tool, forming the cutting layer 12 into a desired shape with high accuracy. When this method is explained in detail by providing specific values, base material of cemented carbide 13 is a cemented carbide material mainly comprising tungsten carbide (WC) of 6 mm diameter and 10 mm thickness which is roughly processed by electrical discharge machining into upper and lower dies having hollow-shaped press surfaces of 1 mm radius of curvature. Cutting layer 12 is formed on top of the roughly processed die with a thickness of about 15µm. By cutting precisely the cutting layer 12, a hollow-shaped die of 1 mm radius of curvature was obtained with high accuracy which was difficult to attain with a conventional grinding process. In addition, this method required only 1/10 of the time needed for a conventional grinding process. Furthermore, the Pt-Ir alloy protective layer 11 is formed with a thickness of 3µm by the sputtering method. This embodiment uses a ternary alloy film as the cutting layer 12. In particular, it is possible to use Ni-P ternary alloys, for example, Ni-Si-P, Ni-Ti-P, Ni-Cu-P, Ni-Zr-P, Ni-Nb-P, Ni-Mo-P, Ni-Ru-P, Ni-Rh-P, Ni-Pd-P, Ni-Hf-P, Ni-Ta-P, Ni-W-P, Ni-Re-P, Ni-Os-P, and Ni-Ir-P. It is also possible to use Co-P ternary alloys, for example, Co-Si-P, Co-Ti-P, Co-Cu-P, Co-Zr-P, Co-Nb-P, Co-Mo-P, Co-Ru-P, Co-Rh-P, Co-Pd-P, Co-Hf-P, Co-Ta-P, Co-W-P, Co-Re-P, Co-Os-P, and Co-Ir-P. Furthermore, Fe-P ternary alloys can also be used, for example, Fe-Si-P, Fe-Ti-P, Fe-Cu-P, Fe-Zr-P, Fe-Nb-P, Fe-Mo-P, Fe-Ru-P, Fe-Rh-P, Fe-Pd-P, Fe-Hf-P, Fe-Ta-P, Fe-W-P, Fe-Re-P, Fe-Os-P, and Fe-Ir-P. In practice, these alloy films can be used as cutting layer 12 when they have about 15µm thickness. For example, the following method is taken to form the above-mentioned alloy films as cutting layer 12 on the surface of a roughly processed die by a sputtering method. First, a Ni-P or Co-P plated layer (percentage content of P= about 12wt%) is formed with a thickness of about 0.5 mm by an electroless plating method on a Ni chip having a size of 10 mm × 10 mm × 1 mm. Thus, a Ni-P chip or a Co-P chip is formed. In order to form a Ni-Si-P alloy film, 40 pieces of the Ni-P chip formed by the above-noted method are arranged equally on top of e.g. a Si disk target having a diameter of 6 inches. The sputtering method is conducted by using this as the target material to form the Ni-Si-P ternary alloy film. In the same way, by arranging 40 pieces of the above-noted chip equally on top of disk targets of Si, Ti, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os or Ir having a diameter of 6 inches and using them as the target materials for the sputtering process, different kinds of ternary alloy films can be formed according to each material of disk target being used. In order to form a Fe-P ternary alloy film, Fe 3 P compound chips having sizes of 10 mm × 10 mm × 1 mm are arranged equally on top of a disk target comprising a material selected from the various materials noted in this example above. In the same way, the sputtering method is conducted by using it as the target material to form different kinds of Fe-P ternary alloy film. In order to conduct the press-molding process by using the die of FIG. 1, this molding die is disposed in a press-molding machine shown in FIG. 2. Referring to FIG. 2, reference numeral 21 denotes a fixing block for an upper die; 22, a heater for the upper die; 23, the upper die; 24, a glass material; 25, a lower die; 26, a heater for the lower die; 27, a fixing block for the lower die; 28, a cover; 29, a body for the die; 210, a plunger; 211, a positioning sensor; 212, a stopper. Then, dense barium crop glass (SK-12) 24 manufactured by SUMITA OPTICAL GLASS, INC. which was processed into a spherical shape having a radius of 1 mm is placed on lower die 25, and upper die 23 is placed on the top. In this condition, the temperature was raised to 650°C, and the pressure was kept at about 40kg/cm 2 in a nitrogen atmosphere for two minutes. After that, the temperate was lowered to 550°C in this condition, and the pressure was then released. After it was cooled to room temperature, the molded glass lens was taken out, and the press-molding process of the glass optical element was completed. After repeating this press-molding process 10,000 times, upper and lower dies 23, 25 were removed from the press-molding machine, and the condition of the press surfaces were observed with an optical microscope. At the same time, the surface roughness (root mean square (RMS) value, nm) of the press surface was measured, and the accuracy of each die was evaluated. The results are shown in Table 1 (a) and (b). In Table 1, "surface condition" refers to the observed results of the optical microscope. The units for surface roughness used in Table 1 are is all nm. Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 2 Ni-Si-P 1.03 1.04 satisfactory 3 Ni-Ti-P 1.01 1.03 satisfactory 4 Ni-Cu-P 1.01 1.02 satisfactory 5 Ni-Zr-P 1.04 1.05 satisfactory 6 Ni-Nb-P 1.02 1.04 satisfactory 7 Ni-Mo-P 1.01 1.02 satisfactory 8 Ni-Ru-P 1.01 1.01 satisfactory 9 Ni-Rh-P 1.03 1.03 satisfactory 10 Ni-Pd-P 1.05 1.06 satisfactory 11 Ni-Hf-P 1.02 1.04 satisfactory 12 Ni-Ta-P 1.02 1.03 satisfactory 13 Ni-W-P 1.05 1.06 satisfactory 14 Ni-Re-P 1.02 1.03 satisfactory 15 Ni-Os-P 1.01 1.01 satisfactory 16 Ni-Ir-P 1.02 1.03 satisfactory 17 Co-Si-P 1.07 1.09 satisfactory 18 Co-Ti-P 1.05 1.08 satisfactory 19 Co-Cu-P 1.03 1.03 satisfactory 20 Co-Zr-P 1.07 1.09 satisfactory 21 Co-Nb-P 1.07 1.10 satisfactory 22 Co-Mo-P 1.06 1.09 satisfactory 23 Co-Ru-P 1.04 1.09 satisfactory 24 Co-Rh-P 1.07 1.08 satisfactory 25 Co-Pd-P 1.05 1.06 satisfactory 26 Co-Hf-P 1.04 1.06 satisfactory 27 Co-Ta-P 1.01 1.01 satisfactory 28 Co-W-P 1.04 1.05 satisfactory 29 Co-Re-P 1.06 1.09 satisfactory 30 Co-Os-P 1.09 1.11 satisfactory 31 Co-Ir-P 1.05 1.08 satisfactory Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 32 Fe-Si-P 1.04 1.05 satisfactory 33 Fe-Ti-P 1.06 1.07 satisfactory 34 Fe-Cu-P 1.03 1.06 satisfactory 35 Fe-Zr-P 1.07 1.09 satisfactory 36 Fe-Nb-P 1.05 1.06 satisfactory 37 Fe-Mo-P 1.08 1.12 satisfactory 38 Fe-Ru-P 1.06 1.07 satisfactory 39 Fe-Rh-P 1.04 1.04 satisfactory 40 Fe-Pd-P 1.05 1.08 satisfactory 41 Fe-Hf-P 1.08 1.09 satisfactory 42 Fe-Ta-P 1.07 1.08 satisfactory 43 Fe-W-P 1.09 1.10 satisfactory 44 Fe-Re-P 1.04 1.09 satisfactory 45 Fe-Os-P 1.06 1.06 satisfactory 46 Fe-Ir-P 1.07 1.09 satisfactory As shown in Table 1, the dies of this embodiment possess long durability which was not possible using conventional materials. This is one of the major characteristics of this invention. A Ni-P binary alloy film was formed as the cutting layer on the base material of cemented carbide by the electroless plating method, and the Pt-Ir alloy film was used as a protective coat to form the die. This die was placed in the press-molding machine shown in FIG. 2. The press-molding process took place under the same conditions as above, and the accuracy of the die wad evaluated. The results of this comparative experiment are shown in Table 2. Results of Comparative Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 100 times Surface roughness (RMS, nm) Surface condition 1 Ni-P plated film 1.03 6.27 Enlarged crack As shown as comparative Sample No. 1 in Table 2, the conventional molding die comprises a cutting layer of electroless Ni-P plated film cut into a transcriptional surface which is then coated with a Pt-Ir alloy film for protection. The glass does not adhere to this die, but the plated surface began to crack after being press-molded several times. After press-molding only 100 times, the crack on the plated surface enlarged more and more. The die did not stand any more use because the crack was transcribed on the lens, thereby deteriorating the quality of the lens. This is due to the fact that Ni-P plated film which was used as the cutting layer did not have sufficient heat resistance so that Ni-P plated film can not withstand the heat cycle of the press-molding process when the glass having a high melting point is press-molded repeatedly. On the other hand, according to the molding dies shown in invention Sample Nos. 2 to No. 46 of Table 1, the dies did not crack even after being press-molded 10,000 times, and the surface condition remained almost the same. In addition, the surface roughness had hardly changed. It shows that these dies can press-mold glass having a high melting point, such as SK-12. The dies in this embodiment have enhanced the free-cutting property by including P in the film material of the cutting layer and improved the heat resistance by forming the cutting layer with materials of ternary alloy films. In this way, all the requirements which are necessary to press-mold the above-mentioned glass optical elements directly with high accuracy were met. It enabled press-molding a large quantity of glass optical elements having high melting points and shapes which was impossible using conventional methods. In this embodiment, cemented carbide mainly consisting of WC was used as the base material of the press-molding die. It goes without saying that any other material can be used to attain the same results as long as the material has heat resistance and sufficient strength to withstand the press-molding process of optical glass. However, it is preferable to use cemented carbide mainly consisting of WC, cermet mainly consisting of TiN or TiC, or WC sintered compact. As far as the protective layer is concerned, Pt-Ir was used in this embodiment, but the same results could be attained by using an alloy film of precious metal which includes at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W and Ta. As a result, by press-molding glass by means of the press-molding die of this invention, it is possible to press-mold a large quantity of glass optical elements having high melting points and shapes which are difficult to attain by a grinding process. Example 2 The dimension and the structure of a die used in this embodiment are exactly the same as in the first embodiment except for the material used for the cutting layer and the protective layer. The same press-molding machine was used as in FIG. 2. The cutting layer used in this embodiment is a Ni-B ternary alloy, a Co-B ternary alloy, or a Fe-B ternary alloy. In particular, it is possible to use Ni-B ternary alloys, for example, Ni-Si-B, Ni-Ti-B, Ni-Cu-B, Ni-Zr-B, Ni-Nb-B, Ni-Mo-B, Ni-Ru-B, Ni-Rh-B, Ni-Pd-B, Ni-Hf-B, Ni-Ta-B, Ni-W-B, Ni-Re-B, Ni-Os-B, and Ni-Ir-B. It is also possible to use Co-B ternary alloys, for example, Co-Si-B, Co-Ti-B, Co-Cu-B, Co-Zr-B, Co-Nb-B, Co-Mo-B, Co-Ru-B, Co-Rh-B, Co-Pd-B, Co-Hf-B, Co-Ta-B, Co-W-B, Co-Re-B, Co-Os-B, and Co-Ir-B. Furthermore, Fe-B ternary alloys can also be used, for example, Fe-Si-B, Fe-Ti-B, Fe-Cu-B, Fe-Zr-B, Fe-Nb-B, Fe-Mo-B, Fe-Ru-B, Fe-Rh-B, Fe-Pd-B, Fe-Hf-B, Fe-Ta-B, Fe-W-B, Fe-Re-B, Fe-Os-B, and Fe-Ir-B. In practice, these alloys can be used to form cutting layers when they are processed with a thickness of about 15µm by the sputtering method. Furthermore, a Pt-Os alloy protective layer is formed with a thickness of 3µm on the cutting layer by the sputtering method. In order to form the cutting layer of ternary alloys on the base material of the molding die, the same procedure as in the first embodiment is used. First, a Ni-B or Co-B plated layer (percentage content Of B= about 12 wt%) is formed with a thickness of about 0.5 mm by an electroless plating method on a Ni chip having a size of 10 mm × 10 mm × 1 mm. Thus, a Ni-B chip or a Co-B chip is formed. Then, 40 pieces of these chips are arranged equally on top of disk targets of Si, Ti, Cu, Zr, Nb, Mo, Ru, Rh, Bd, Hf, Ta, W, Re, Os or Ir having a diameter of 6 inches. They are used as the target materials in the sputtering process. In order to form a cutting layer of Fe-B ternary alloys, 40 pieces of Fe-B compound chips having sizes of 10 mm × 10 mm × 1 mm are arranged equally on top of disk targets consisting of the various materials mentioned above to form different kinds of ternary alloy films. Similarly, these alloy films were formed into transcription surfaces with high accuracy using a diamond tool. A cross-sectional view of the die for press-molding glass optical elements produced by this method is shown in FIG. 3 where Ni-Ti-B alloy film is used as the cutting layer. Referring to FIG. 3, reference numeral 31 denotes a Pt-Os alloy protective layer covering the press surface; 32, a Ni-Ti-B alloy cutting layer; and 33, a base material of cemented carbide. These dies are placed in the press-molding machine shown in FIG. 2. Then, dense barium crown glass (SK-12) which was processed into a spherical shape having a radius of 1 mm was molded under the same molding conditions as in the first example. After repeating this press-molding process 10,000 times, upper and lower dies 23, 25 were removed from the press-molding machine and the condition of the press surfaces were observed with an optical microscope. And then, the surface roughness (RMS value, nm) of the press surface was measured, and the accuracy of each die was evaluated. The results are shown in Table 4 (a) and (b). Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 48 Ni-Si-B 1.05 1.07 satisfactory 49 Ni-Ti-B 1.04 1.05 satisfactory 50 Ni-Cu-B 1.04 1.05 satisfactory 51 Ni-Zr-B 1.04 1.05 satisfactory 52 Ni-Nb-B 1.02 1.04 satisfactory 53 Ni-Mo-B 1.06 1.07 satisfactory 54 Ni-Ru-B 1.01 1.03 satisfactory 55 Ni-Rh-B 1.05 1.06 satisfactory 56 Ni-Pd-B 1.06 1.07 satisfactory 57 Ni-Hf-B 1.03 1.04 satisfactory 58 Ni-Ta-B 1.02 1.03 satisfactory 59 Ni-W-B 1.02 1.03 satisfactory 60 Ni-Re-B 1.04 1.05 satisfactory 61 Ni-Os-B 1.06 1.07 satisfactory 62 Ni-Ir-B 1.04 1.05 satisfactory 63 Co-Si-B 1.01 1.02 satisfactory 64 Co-Ti-B 1.03 1.04 satisfactory 65 Co-Cu-B 1.02 1.03 satisfactory 66 Co-Zr-B 1.05 1.08 satisfactory 67 Co-Nb-B 1.01 1.13 satisfactory 68 Co-Mo-B 1.04 1.05 satisfactory 69 Co-Ru-B 1.02 1.03 satisfactory 70 Co-Rh-B 1.02 1.03 satisfactory 71 Co-Pd-B 1.02 1.04 satisfactory 72 Co-Hf-B 1.04 1.06 satisfactory 73 Co-Ta-B 1.05 1.06 satisfactory 74 Co-W-B 1.04 1.05 satisfactory 75 Co-Re-B 1.01 1.04 satisfactory 76 Co-Os-B 1.08 1.11 satisfactory 77 Co-Ir-B 1.06 1.08 satisfactory Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 78 Fe-Si-B 1.05 1.06 satisfactory 79 Fe-Ti-B 1.04 1.05 satisfactory 80 Fe-Cu-B 1.03 1.04 satisfactory 81 Fe-Zr-B 1.04 1.05 satisfactory 82 Fe-Nb-B 1.05 1.06 satisfactory 83 Fe-Mo-B 1.03 1.03 satisfactory 84 Fe-Ru-B 1.02 1.03 satisfactory 85 Fe-Rh-B 1.04 1.06 satisfactory 86 Fe-Pd-B 1.06 1.08 satisfactory 87 Fe-Hf-B 1.07 1.08 satisfactory 88 Fe-Ta-B 1.02 1.04 satisfactory 89 Fe-W-B 1.05 1.06 satisfactory 90 Fe-Re-B 1.04 1.06 satisfactory 91 Fe-Os-B 1.06 1.06 satisfactory 92 Fe-Ir-B 1.07 1.09 satisfactory Furthermore, a comparative experiment was conducted. A Ni-B binary alloy film was formed as the cutting layer on the base material of cemented carbide by the electroless plating method, and the Pt-Os alloy film as in this embodiment was used as a protective layer to form the die. The same press-molding process took place as in this embodiment, and the accuracy of the die was evaluated. The results of this comparative experiment are shown in Table 3. Results of Comparative Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 100 times Surface roughness (RMS, nm) Surface condition 47 Ni-B plated film 1.03 6.84 Enlarged crack As shown in comparative Sample No. 47, the die comprises binary alloy plated film of eletroless Ni-B as the cutting layer which is then coated with a Pt-Os alloy film. The glass does not adhere to this die, but the plated film began to crack after being press-molded several times. After press-molding 100 times, the crack on the plated surface enlarged. The die did not stand any more use because the crack was transcribed on the lens, thereby deteriorating the quality of the lens. This is due to the fact that Ni-B binary alloy film which was used as the cutting layer did not have sufficient heat resistance to withstand the heat cycle of the press-molding process when the glass having a high melting point is press-molded repeatedly. On the other hand, according to the dies of this invention shown in invention Sample Nos. 48 to No. 92, the dies did not crack even after press-molded 10,000 times and the surface condition remained almost the same. In addition the surface roughness had hardly changed. It shows that these dies can press-mold glass having a high melting point, such as SK-12. As a result, by press-molding glass by means of the press-molding of this invention, it is possible to press-mold a large quantity of glass optical elements having high melting points and shapes which are difficult to attain by a grinding process. As described above, the dies in this embodiment have enhanced the free-cutting property by including B in the cutting alloy layer and improved the heat resistance by forming ternary alloy films. In this way, all the requirements which are necessary to press-mold directly the above-mentioned glass optical elements with high accuracy were met. It enabled press-molding a large quantity of glass optical elements having high melting points and shapes which was impossible to be molded by conventional methods. Cemented carbide mainly consisting of WC was used as the base material or the die for press-molding in this embodiment. It goes without saying that any other material can be used to attain the same results provided that it has heat resistance and sufficient strength to withstand the press-molding process for optical glass. However, it is preferable to use cemented carbide consisting mainly of WC, cermet mainly consisting of TiN or TiC, or WC sintered compact. As far as the protective layer is concerned, Pt-Os was used in this embodiment, but the same results could be attained by using an alloy film of precious metal which includes at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W and Ta. Example 3 [Not falling within the scope of the claims of this invention] The die for press-molding of this example is exactly the same as in the first embodiment except for the composition of material used for the alloy cutting layer and the protective layer. The cutting layer used is a Cu binary alloy layer. In particular, suitable Cu binary alloys include, for example, Cu-Ni, Cu-Co, Cu-Fe, Cu-Si, Cu-Ti, Cu-Zr, Cu-Nb, Cu-Mo, Cu-Ru, Cu-Rh, Cu-Pd, Cu-Hf, Cu-Ta, Cu-W, Cu-Re, and Cu-Os. In order to form these binary alloy films, a Cu chip having a size of 10 mm × 10 mm × 1 mm is arranged equally on top of disk targets of Ni, Co, Fe, Si, Ti, Zr, Nb Mo, Ru, Rh, Pd, Hf, Ta, W, Re or Os having a diameter of 15 cm (6 inches). These are used as the target material for the sputtering process. At the same time, by changing the number of the Cu-chips arranged on the disk targets, it is possible to control the composition of Cu binary alloys being formed. A Pt-Rh alloy protective layer was formed with a thickness of 3µm on the cutting layer by the sputtering method. The thickness of the cutting layer consisting of the Cu binary alloy was determined to be about 15µm. A cross-sectional view of the die for press-molding is shown in FIG. 4. Referring to FIG. 4, reference numeral 41 denotes a Pt-Rh alloy protective layer covering the press surface; 42, a Cu-Ti alloy cutting film; 43, a base material of cemented carbide. These dies are placed in the press-molding machine shown in FIG. 2. Then, dense barium crown glass (SK-12) 24 which was processed into a spherical shape with a radius of 1 mm was press-molded under the same conditions as in the first embodiment. After repeating this press-molding process 10,000 times, upper and lower dies 23, 25 were removed from the press-molding machine, and the condition of the press surfaces was observed with an optical microscope. At this moment, surface roughness (RMS value, nm) of the press surface was measured, and the accuracy of each die was evaluated. The results are shown in Table 6 (a) and (b). The percentage content of Cu in the composition was controlled within the range of 20 to 80 at %. This is due to the fact that a diamond tool is worn when used for cutting with a Cu content of less than 20 at %, while the shape is deformed when pressed with Cu content of more than 80 at % due to hardness deterioration. As mentioned above, the percentage content of Cu was controlled by changing the number of the Cu-chips arranged on disk targets. Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 94 Cu(20)-Ni(80) 1.03 1.04 satisfactory 95 Cu(50)-Ni(50) 1.05 1.07 satisfactory 96 Cu(80)-Ni(20) 1.04 1.05 satisfactory 97 Cu(20)-Co(80) 1.07 1.08 satisfactory 98 Cu(50)-Co(50) 1.03 1.04 satisfactory 99 Cu(80)-Co(20) 1.04 1.05 satisfactory 100 Cu(20)-Fe(80) 1.06 1.07 satisfactory 101 Cu(50)-Fe(50) 1.03 1.05 satisfactory 102 Cu(80)-Fe(20) 1.02 1.03 satisfactory 103 Cu(20)-Si(80) 1.05 1.06 satisfactory 104 Cu(50)-Si(50) 1.04 1.05 satisfactory 105 Cu(80)-Si(20) 1.06 1.08 satisfactory 106 Cu(20)-Ti(80) 1.05 1.07 satisfactory 107 Cu(50)-Ti(50) 1.04 1.05 satisfactory 108 Cu(80)-Ti(20) 1.06 1.07 satisfactory 109 Cu(20)-Zr(80) 1.03 1.04 satisfactory 110 Cu(50)-Zr(50) 1.05 1.07 satisfactory 111 Cu(80)-Zr(20) 1.01 1.04 satisfactory 112 Cu(20)-Nb(80) 1.07 1.08 satisfactory 113 Cu(50)-Nb(50) 1.04 1.05 satisfactory 114 Cu(80)-Nb(20) 1.01 1.03 satisfactory 115 Cu(20)-Mo(80) 1.05 1.06 satisfactory Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 116 Cu(50)-Mo(50) 1.04 1.04 satisfactory 117 Cu(80)-Mo(20) 1.05 1.07 satisfactory 118 Cu(20)-Ru(80) 1.05 1.06 satisfactory 119 Cu(50)-Ru(50) 1.05 1.06 satisfactory 120 Cu(80)-Ru(20) 1.07 1.08 satisfactory 121 Cu(20)-Rh(80) 1.03 1.04 satisfactory 122 Cu(50)-Rh(50) 1.08 1.09 satisfactory 123 Cu(80)-Rh(20) 1.05 1.07 satisfactory 124 Cu(20)-Pd(80) 1.03 1.05 satisfactory 125 Cu(50)-Pd(50) 1.06 1.07 satisfactory 126 Cu(80)-Pd(20) 1.01 1.03 satisfactory 127 Cu(20)-Hf(80) 1.06 1.08 satisfactory 128 Cu(50)-Hf(50) 1.06 1.06 satisfactory 129 Cu(80)-Hf(20) 1.07 1.09 satisfactory 130 Cu(20)-Ta(80) 1.02 1.05 satisfactory 131 Cu(50)-Ta(50) 1.03 1.06 satisfactory 132 Cu(80)-Ta(20) 1.04 1.05 satisfactory 133 Cu(20)-W (80) 1.02 1.04 satisfactory 134 Cu(50)-W (50) 1.06 1.07 satisfactory 135 Cu(80)-W (20) 1.05 1.08 satisfactory 136 Cu(20)-Re(80) 1.01 1.03 satisfactory 137 Cu(50)-Re(50) 1.04 1.06 satisfactory 138 Cu(80)-Re(20) 1.05 1.05 satisfactory 139 Cu(20)-Os(80) 1.07 1.08 satisfactory 140 Cu(50)-Os(50) 1.01 1.03 satisfactory 141 Cu(80)-Os(20) 1.05 1.07 satisfactory Furthermore, a comparative experiment was conducted. As in the first embodiment, a Ni-P film was formed as the cutting layer on the base material of cemented carbide by the electroless plating method, and the Pt-Rh alloy film was used as a protective layer to form the die. The press-molding process took place repeatedly under exactly the same molding conditions. The results of this experiment are shown in Table 5. Results of Comparative Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 100 times Surface roughness (RMS, nm) Surface condition 93 Ni-P plated film 1.03 7.19 Enlarged crack When the die used in comparative sample No. 93 was used for molding, the glass did not adhere to the die, but the plated layer began to crack after being press-molded several times. After press-molding 100 times, the crack on the plated surface enlarged. The die did not stand any more use because the crack was transcribed on the lens, thereby deteriorating the quality of the lens. This is due to the fact that Ni-P plated film which was used as the cutting layer did not have sufficient heat resistance to withstand the heat cycle of the press-molding process when the glass having a high melting point is press-molded repeatedly. On the other hand, according to the dies shown in Sample Nos. 94 to No. 141, the dies did not crack even after being press-molded 10,000 times, and the surface condition remained almost the same. The surface roughness has hardly changed. It shows that these dies can press-mold glass having a high melting point, such as SK-12. As a result, by press-molding glass by means of the press-molding of this example, it is possible to press-mold a large quantity of glass optical elements having high melting points and shapes which are difficult to attain by a grinding process. Accordingly, all the requirements which are necessary to directly press-mold the above-mentioned glass optical elements with high accuracy were met. It enabled press-molding a large quantity of glass optical elements having high melting points and shapes which was impossible using conventional methods. Cemented carbide consisting mainly of WC was used as the base material of the die for press-molding. It goes without saying that any other material can be used to attain the same results as long as it has heat resistance and sufficient strength to withstand the press-molding process of optical glass. However, it is preferable to use cemented carbide consisting mainly of WC, cermet consisting mainly of TiN or TiC, or WC sintered compact. As far as the protective layer is concerned, Pt-Rh was used in this embodiment, but the same results could be attained by using an alloy film of precious metal which includes at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W and Ta. Example 4 [Not falling within the scope of the claims of this invention] The die for press-molding in this example is exactly the same as in the first embodiment except for the composition of material used for the alloy cutting layer and the protective layer. The cutting layer used is a Si binary alloy layer. In particular, it is possible to use Si binary alloys for the cutting layer, for example, Si-Ni, Si-Co, Si-Fe, Si-Si, Si-Ti, Si-Zr, Si-Nb, Si-Mo, Si-Ru, Si-Rh, Si-Pd, Si-Hf, Si-Ta, Si-W, Si-Re, and Si-Os. In order to form these binary alloy films, a Si chip having a size of 10 mm × 10 mm × 1 mm is arranged equally on disk targets of Ni, Co, Fe, Si, Ti, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re or Os having a diameter of 15 cm (6 inches). These are used as the target material in the sputtering process. By changing the number of the Si chips arranged on the disk targets, it is possible to control the composition of Si binary alloys being formed. A Pt-Rh alloy protective layer was formed with a thickness of 3µm on the cutting layer by the sputtering method. The thickness of the cutting layer consisting of Si binary alloys was determined to be about 15µm. A cross-sectional view of the die for press-molding is shown in FIG. 5. Referring to FIG. 5, reference numeral 51 denotes a Pt-Pd alloy protective layer covering the press surface; 52, a Si-Ta alloy cutting film; 53, a base material of cemented carbide. These dies are placed in the press-molding machine shown in FIG. 2. Then, dense barium crown glass (SK-12) 24 which was processed into a spherical shape with a radius of 1 mm was press-molded under the same conditions as in the first embodiment. After repeating this press-molding process 10,000 times, upper and lower dies 23, 25 were removed from the press-molding machine and the condition of the press surfaces was observed with an optical microscope. At the same time, the surface roughness (RMS value, nm) of the press surface was measured, and the accuracy of each die was evaluated. The results are shown in Table 8 (a) to (c). The percentage content of Si in the composition was controlled within the range of 20 to 80 at %. This is due to the fact that a diamond tool is worn when used for cutting with a Si content of less than 20 at %, while the shape is deformed when pressed with a Si content of more than 80 at % due to hardness deterioration. As described above, the percentage content of Si in the cutting layer was changed by controlling the number of the Si chips arranged on the disk targets. Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 143 Si(20)-Ni(80) 1.03 1.04 satisfactory 144 Si(50)-Ni(50) 1.05 1.07 satisfactory 145 Si(80)-Ni(20) 1.04 1.05 satisfactory 146 Si(20)-Co(80) 1.07 1.08 satisfactory 147 Si(50)-Co(50) 1.03 1.04 satisfactory 148 Si(80)-Co(20) 1.04 1.05 satisfactory 149 Si(20)-Fe(80) 1.06 1.07 satisfactory 150 Si(50)-Fe(50) 1.03 1.05 satisfactory 151 Si(80)-Fe(20) 1.02 1.03 satisfactory 152 Si(20)-Cu(80) 1.05 1.06 satisfactory 153 Si(50)-Cu(50) 1.03 1.05 satisfactory 154 Si(80)-Cu(20) 1.05 1.07 satisfactory 155 Si(20)-Ti(80) 1.08 1.09 satisfactory 156 Si(50)-Ti(50) 1.06 1.08 satisfactory 157 Si(80)-Ti(20) 1.03 1.06 satisfactory 158 Si(20)-Zr(80) 1.03 1.04 satisfactory 159 Si(50)-Zr(50) 1.04 1.07 satisfactory 160 Si(80)-Zr(20) 1.02 1.06 satisfactory 161 Si(20)-Nb(80) 1.07 1.08 satisfactory 162 Si(50)-Nb(50) 1.06 1.08 satisfactory 163 Si(80)-Nb(20) 1.04 1.07 satisfactory Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 164 Si(20)-Mo(80) 1.02 1.05 satisfactory 165 Si(50)-Mo(50) 1.07 1.08 satisfactory 166 Si(80)-Mo(20) 1.05 1.08 satisfactory 167 Si(20)-Ru(80) 1.04 1.05 satisfactory 168 Si(50)-Ru(50) 1.01 1.03 satisfactory 169 Si(80)-Ru(20) 1.04 1.06 satisfactory 170 Si(20)-Rh(80) 1.05 1.07 satisfactory 171 Si(50)-Rh(50) 1.04 1.06 satisfactory 172 Si(80)-Rh(20) 1.03 1.05 satisfactory 173 Si(20)-Pd(80) 1.04 1.07 satisfactory 174 Si(50)-Pd(50) 1.03 1.05 satisfactory 175 Si(80)-Pd(20) 1.03 1.06 satisfactory 176 Si(20)-Hf(80) 1.04 1.05 satisfactory 178 Si(50)-Hf(50) 1.06 1.07 satisfactory 179 Si(80)-Hf(20) 1.05 1.08 satisfactory 180 Si(20)-Ta(80) 1.04 1.07 satisfactory 181 Si(50)-Ta(50) 1.04 1.06 satisfactory 182 Si(80)-Ta(20) 1.04 1.05 satisfactory 183 Si(20)-W (80) 1.02 1.04 satisfactory 184 Si(50)-W (50) 1.06 1.07 satisfactory 185 Si(80)-W (20) 1.05 1.08 satisfactory 186 Si(20)-Re(80) 1.01 1.03 satisfactory 187 Si(50)-Re(50) 1.04 1.06 satisfactory 188 Si(80)-Re(20) 1.05 1.05 satisfactory Furthermore, a comparative experiment was conducted. As in the first embodiment, a Ni-P plated film was formed as the cutting layer on the base material of cemented carbide by the electroless plating method, and the Pt-Pd alloy film was used as a protective layer to form the die. The press-molding process took place repeatedly under exactly the same press-molding conditions. The results of this experiment are shown in Table 7. Results of Comparative Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 100 times Surface roughness (RMS, nm) Surface condition 142 Ni-P plated film 1.03 5.96 Enlarged crack When the die used in comparative Sample No. 142 was molded, the glass did not adhere to this die, but the plated layer began to crack after press-molded several times. After press-molding 100 times, the crack on the plated surface enlarged. The die did not stand any more use because the crack was transcribed on the lens, thereby deteriorating the quality of the lens. This is due to the fact that Ni-P plated film which was used as the cutting layer has not sufficient heat resistance to withstand the heat cycle of the press-molding process when the glass having a high melting point is press-molded repeatedly. On the other hand, according to the dies shown in Sample Nos. 143 to No. 191, the dies did not crack even after press-molded 10,000 times and the surface condition remained almost the same. The surface roughness has hardly changed. It shows that these dies can press-mold glass having a high melting point, such as SK-12. As a result, by press-molding glass by means of the press-molding of this example, it is possible to press-mold a large quantity of glass optical elements having high melting points and shapes which are difficult to attain by a grinding process. Accordingly, all the requirements which are necessary to directly press-mold the above-mentioned glass optical elements with high accuracy were met. It enabled to press-mold a large quantity of glass optical elements having high melting points and shapes which were impossible to be molded in the past. Cemented carbide consisting mainly of WC was used as the base material of the die for press-molding. It goes without saying that any other material can be used to attain the same results that has heat resistance and sufficient strength to withstand the press-molding process of optical glass. However, it is preferable to use cemented carbide consisting mainly of WC, cermet mainly consisting of TiN or TiC, or WC sintered compact. As far as the protective layer is concerned, Pt-Pd was used in this example, but the same results could be attained by using an alloy film of precious metal which includes at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W and Ta. Example 5 [Not falling within the scope of the claims of this invention] The dimension and the structure of the die used in this example are exactly the same as in the first embodiment except for the material used for the cutting layer and the protective layer. The same press-molding machine was used as in FIG. 2. In this embodiment, an amorphous binary alloy layer is used as the cutting layer consisting of Ni, Co, Cr, Ta, Mo, Ti, W, Nb, V or Cu. As for an amorphous binary alloy layer with Ni, suitable Ni alloys include, for example, Ni-Co, Ni-Cr, Ni-Ta, Ni-Mo, Ni-Ti, Ni-W, Ni-Nb, Ni-V, Ni-Cu, and Ni-Al. As for an amorphous binary alloy layer with Co, suitable Co alloys include, for example, Co-Cr, Co-Ta, Co-Mo, Co-Ti, Co-W, Co-Nb, Co-V, Co-Cu, and Co-Al. As for an amorphous binary alloy layer with Cr, suitable Cr alloys include, for example, Cr-Ta, Cr-Mo, Cr-Ti, Cr-W, Cr-Nb, Cr-V, Cr-Cu, and Cr-Al. As for an amorphous binary alloy layer with Ta, suitable Ta alloys include, for example, Ta-Mo, Ta-Ti, Ta-W, Ta-Nb, Ta-V, Ta-Cu, and Ta-Al. As for an amorphous binary alloy layer with Mo, suitable Mo alloys include, for example, Mo-Ti, Mo-W, Mo-Nb, Mo-V, Mo-Cu, and Mo-Al. As for an amorphous binary alloy layer with Ti, suitable Ti alloys include, for example, Ti-W, Ti-Nb, Ti-V, Ti-Cu, and Ti-Al. As for an amorphous binary alloy layer with W, suitable W alloys include, for example, W-Nb, W-V, W-Cu, and W-Al. As for an amorphous binary alloy layer with Nb, suitable Nb alloys include, for example, Nb-V, Nb-Cu, and Nb-Al. As for an amorphous binary alloy layer with V, suitable V alloys include, for example, V-Cu and V-Al. As for an amorphous binary alloy layer with Cu, suitable Cu alloys include, for example, Cu-Al alloy film. The reason for putting the cutting layer in an amorphous condition is that a grain boundary will not be present in the cutting layer in this condition. As a result, the cutting property of the cutting layer improves considerably, and the cutting tools will not be worn so much, thereby conducting the cutting process with high accuracy. The above-mentioned amorphous alloy film was cut with use of a diamond tool forming into an extremely accurate surface. By cutting the amorphous alloy film in this way, a hollow-shaped die of 1 mm radius of curvature was obtained with high accuracy which was difficult to attain with a conventional grinding process. In addition, this method required only 1/10 of the time needed for the conventional grinding process. In practice, these amorphous alloys can be used to form cutting layers of molding dies when they are processed with a thickness of about 15µm by the sputtering method. Furthermore, a Pt-Ru alloy protective layer was formed with a thickness of 3µm on the cutting layer by the sputtering method in this embodiment. A cross-sectional view of a die for press-molding produced in this way is shown in FIG. 6 in which a Cr-Cu alloy film is used for the cutting layer. Referring to FIG. 6, reference numeral 61 denotes a Pt-Ru alloy protective layer covering the press surface; 62, a Cr-Cu alloy cutting film; 63, a base material of cemented carbide. These dies are placed in the press-molding machine shown in FIG. 2. Then, dense barium crown glass (SK-12) 24 which was processed into a spherical shape with a radius of 1 mm was molded under the same conditions as in all the above-mentioned embodiments. After repeating this press-molding process 10,000 times, upper and lower dies 23, 25 were removed from the press-molding machine, and the condition of the press surfaces was observed with an optical microscope. At this moment, the surface roughness (RMS value, nm) of the press surface was measured, and the accuracy of each die was evaluated. The results are shown in Table 10 (a), (b) and (c). Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 193 Ni-Co 1.06 1.07 satisfactory 194 Ni-Cr 1.04 1.08 satisfactory 195 Ni-Ta 1.09 1.13 satisfactory 196 Ni-Mo 1.07 1.09 satisfactory 197 Ni-Ti 1.03 1.05 satisfactory 198 Ni-W 1.04 1.08 satisfactory 199 Ni-Nb 1.08 1.09 satisfactory 200 Ni-V 1.08 1.12 satisfactory 201 Ni-Cu 1.03 1.07 satisfactory 202 Ni-Al 1.04 1.06 satisfactory 203 Co-Cr 1.08 1.10 satisfactory 204 Co-Ta 1.05 1.09 satisfactory 205 Co-Mo 1.04 1.06 satisfactory 206 Co-Ti 1.03 1.06 satisfactory 207 Co-W 1.02 1.07 satisfactory 208 Co-Nb 1.01 1.05 satisfactory 209 Co-V 1.06 1.08 satisfactory 210 Co-Cu 1.06 1.09 satisfactory 211 Co-Al 1.04 1.06 satisfactory 212 Cr-Ta 1.03 1.06 satisfactory 213 Cr-Mo 1.04 1.08 satisfactory Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 214 Cr-Ti 1.02 1.06 satisfactory 215 Cr-W 1.04 1.05 satisfactory 216 Cr-Nb 1.03 1.07 satisfactory 217 Cr-V 1.06 1.08 satisfactory 218 Cr-Cu 1.06 1.06 satisfactory 219 Cr-Al 1.04 1.05 satisfactory 220 Ta-Mo 1.06 1.08 satisfactory 221 Ta-Ti 1.05 1.08 satisfactory 222 Ta-W 1.05 1.06 satisfactory 223 Ta-Nb 1.04 1.09 satisfactory 224 Ta-V 1.05 1.07 satisfactory 225 Ta-Cu 1.02 1.06 satisfactory 226 Ta-Al 1.05 1.08 satisfactory 227 Mo-Ti 1.04 1.07 satisfactory 228 Mo-W 1.03 1.04 satisfactory 229 Mo-Nb 1.04 1.09 satisfactory 230 Mo-V 1.09 1.15 satisfactory 231 Mo-Cu 1.06 1.08 satisfactory 232 Mo-Al 1.05 1.08 satisfactory 233 Ti-W 1.01 1.06 satisfactory 234 Ti-Nb 1.07 1.08 satisfactory 235 Ti-V 1.07 1.09 satisfactory 236 Ti-Cu 1.01 1.05 satisfactory 237 Ti-Al 1.06 1.10 satisfactory 238 W -Nb 1.07 1.09 satisfactory 239 W -V 1.07 1.08 satisfactory 240 W -Cu 1.04 1.09 satisfactory 241 W -Al 1.04 1.07 satisfactory 242 Nb-V 1.02 1.06 satisfactory 243 Nb-Cu 1.06 1.08 satisfactory Results of Press Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 10,000 times Surface roughness (RMS, nm) Surface condition 244 Nb-Al 1.04 1.07 satisfactory 245 V -Cu 1.04 1.06 satisfactory 246 V -Al 1.05 1.08 satisfactory 247 Cu-Al 1.08 1.12 satisfactory Furthermore, a comparative experiment was conducted in which crystalline films consisting of Ni-Co, Ni-Cr, Ni-Ta, Ni-Mo, Ni-Ti, Ni-W, Ni-Nb, Ni-V, Ni-Cu, Ni-Al, Co-Cr, Co-Ta, Co-Mo, Co-Ti, Co-W, Co-Nb, Co-V, Co-Cu, Co-Al , Cr-Ta, Cr-Mo, Cr-Ti, Cr-W, Cr-Nb, Cr-V, Cr-Cu, Cr-Al, Ta-Mo, Ta-Ti, Ta-W, Ta-Nb, Ta-V, Ta-Cu, Ta-Al, Mo-Ti, Mo-W, Mo-Nb, Mo-V, Mo-Cu, Mo-Al, Ti-W, Ti-Nb, Ti-V, Ti-Cu, Ti-Al, W-Nb, W-V, W-Cu, W-Al, Nb-V, Nb-Cu, Nb-Al, V-Cu, V-Al, and Cu-Al were formed on the base material of cemented carbide to conduct the cutting process. However, due to the strong cutting force and attrition of tools, it was not possible to form the desired shape. Therefore, a Ni-P plated film was formed as the cutting layer on the base material of cemented carbide by the electroless plating method and Pt-Ru alloy film was used as the protective layer for the die as in the first embodiment. The same press-molding process was performed repeatedly, and the accuracy of each die was evaluated. The results are shown in Table 9. Results of Comparative Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 100 times Surface roughness (RMS, nm) Surface condition 192 Ni-P plated film 1.04 8.41 Enlarged crack When the die used in comparative Sample No. 192 was press-molded, the glass did not adhere to this die, but the plated layer began to crack after being press-molded several times. After press-molding 100 times, the crack on the plated surface enlarged. The die did not stand any more use because the crack was transcribed on the lens, thereby deteriorating the quality of the lens. This is due to the fact that Ni-P plated film which was used as the cutting layer did not have sufficient heat resistance to withstand the heat cycle of the press-molding process when the glass having a high melting point is press-molded repeatedly. On the other hand, according to the dies of this invention shown in Sample Nos. 193 to No. 247, the dies did not crack even after press-molded 10,000 times and the surface condition remained almost the same. The surface roughness has hardly changed. It shows that these dies can press-mold glass having a high melting point, such as SK-12. As a result, by press-molding glass by means of the press-molding glass of this example, it is possible to press-mold a large quantity of glass optical elements having high melting points and shapes which are difficult to attain by a grinding process. Accordingly, all the requirements which are necessary to press-mold the above-mentioned glass optical elements directly with high accuracy were met. It enabled press-molding a large quantity of glass optical elements having high melting points and shapes which was impossible using conventional methods. Cemented carbide consisting mainly of WC was used as the base material of the die for press-molding. It goes without saying that any other material can be used to attain the same results provided that it has heat resistance and sufficient strength to withstand the press-molding process of optical glass. However, it is preferable to use cemented carbide consisting mainly of WC, cermet consisting mainly of TiN or TiC, or WC sintered compact. As far as the protective layer is concerned, Pt-Pd was used in this example, but the same results could be attained by using an alloy film of precious metal which includes at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W and Ta. Example 6 [Falling within the scope of the claims of this invention in part] A die for press-molding in this embodiment has an intermediate layer on the surface on which an alloy cutting layer and a protective layer are formed. The dimensions of the die are the same as in the first embodiment. In this embodiment, it is possible to use, for example, films of Ni, SiC, TiN, and Ta 2 O 5 . In practice, an intermediate layer can be used when it is formed with a thickness of about 1 µm by the sputtering method and so forth. As for the cutting layer, it is possible to use, for example, as embodiments of the invention an alloy film of Ni-W-P or Ni-Cu-B; other examples described using Cu-Ti, Si-Zr or amorphous alloy films of Ni-Mo do not fall within the scope of the claims of this invention. These cutting layers are applicable when they are formed with a thickness of 15µm by the sputtering method. The alloy cutting layer can be cut into a surface with extreme accuracy with use of a diamond tool. By cutting the alloy film in this way, a hollow-shaped die of 1 mm radius of curvature could be obtained with extreme accuracy which was difficult to attain in a conventional grinding process. In addition, this method required only 1/10 of the time needed for the conventional grinding process. A Pt-Ta alloy protective layer was formed with a thickness of 3µm on the cutting layer by the sputtering method. A cross-sectional view of a die for press-molding produced in this way is shown in FIG. 7 in which a SiC film is used for the intermediate layer and a Cu-Ti alloy film for the cutting layer. Referring to FIG. 7, reference numeral 71 denotes a Pt-Ta alloy protective layer covering the press surface; 72, a Cu-Ti alloy cutting film; 73, a SiC film; and 74, a base material of cemented carbide. This die was used to press-mold dense barium crown glass (SK-12) 24 which was processed into a spherical shape having a radius of 1 mm under the same conditions as in the first embodiment. After repeating this press-molding process 10,000 times, 30,000 times, and 50,000 times, upper and lower dies 23, 25 were removed from the press-molding machine, and the condition of the press surfaces was observed with an optical microscope. At the same time, the surface roughness (RMS value, nm) of the press surface was measured, and the accuracy of each die was evaluated. The results are shown in Table 12. Results of Press Experiment Sample No. Type of die intermediate layer Surface roughness before pressing (RMS,nm) Surface condition after pressing 10,000 times (RMS,nm) 30,000 times (RMS,nm) 50,000 times (RMS,nm) 254 Ni-W-P Ni 1.05 1.07 1.08 1.09 255 Ni-W-P SiC 1.06 1.06 1.08 1.08 256 Ni-W-P TiN 1.03 1.04 1.04 1.05 257 Ni-W-P Ta2O5 1.06 1.07 1.09 1.01 258 Ni-Cu-B Ni 1.04 1.06 1.08 1.09 259 Ni-Cu-B SiC 1.04 1.05 1.06 1.07 260 Ni-Cu-B TiN 1.02 1.03 1.05 1.08 261 Ni-Cu-B Ta2O5 1.04 1.04 1.07 1.08 262 Cu-Ti Ni 1.04 1.05 1.07 1.09 263 Cu-Ti SiC 1.04 1.06 1.07 1.08 264 Cu-Ti TiN 1.03 1.03 1.06 1.07 265 Cu-Ti Ta2O5 1.03 1.04 1.06 1.06 266 Si-Zr Ni 1.04 1.05 1.07 1.10 267 Si-Zr SiC 1.06 1.07 1.08 1.09 268 Si-Zr TiN 1.05 1.05 1.06 1.08 269 Si-Zr Ta2O5 1.05 1.06 1.08 1.09 270 Ni-Mo Ni 1.04 1.05 1.07 1.08 271 Ni-Mo SiC 1.04 1.05 1.07 1.09 272 Ni-Mo TiN 1.03 1.03 1.05 1.07 273 Ni-Mo Ta2O5 1.04 1.05 1.06 1.07 As a comparative experiment, a Ni-P plated film was formed as the cutting layer on a base material of cemented carbide by the electroless plating method, and Pt-Ta alloy film was used as a protective layer to form the die. The same press-molding process took place, and the accuracy of each die was evaluated. The results are shown in Table 11. Results of Comparative Experiment Sample No. Type of die Surface roughness before pressing (RMS, nm) After pressing 100 times Surface roughness (RMS, nm) Surface condition 248 Ni-P plated film 1.07 5.49 Transcribed crack When the molding die of comparative Sample No. 248 was molded, the glass did not adhere to this die, but the plated layer began to crack after press-molded several times. After press-molding 100 times, the crack on the plated surface enlarged. The die did not stand any more use because the crack was transcribed on the lens, thereby deteriorating the quality of the lens. Furthermore, the die in this embodiment has characteristics superior to the dies shown in the embodiments 1 to 5, as shown in the following. As the cutting layers in the embodiments 1 to 5 (i.e., Example 1 to 5), alloy films of Ni-W-P, Ni-Cu-B, Cu-Ti, Si-Zr, and Ni-Mo amorphous alloy films were formed using Pt-Ta alloy film as a protective layer. After press-molding these dies 10,000 times, 30,000 times and 40,000 times, the condition of the press surfaces was observed with an optical microscope. At the same time, the surface roughness (RMS value, nm) of the press surfaces were measured, and the accuracy of each die was evaluated. The results are shown in Table 13. Results of Comparative Experiment Sample No. Type of die Surface roughness before pressing (RMS,nm) Surface condition after pressing 10,000 times (RMS,nm) 30,000 times (RMS,nm) 40,000 times (RMS,nm) 249 Ni-W-P 1.04 1.13 2.06 Peeled 250 Ni-Cu-B 1.02 1.09 1.87 Peeled 251 Cu-Ti 1.05 1.12 2.07 Peeled 252 Si-Zr 1.02 1.08 1.94 Peeled 253 Ni-Mo 1.04 1.10 2.01 Peeled In the Sample Nos. 249 to 253, the molding dies did not have rough surfaces, and the films did not peel or crack even after press-molded 30,000 times repeatedly. This shows the superior characteristics compared to the conventional dies. However, the films peeled off from the base material when press-molded 40,000 times so that the process had to be stopped then. On the other hand, the dies in the Sample Nos. 254 to 273 of this embodiment did not crack even after being press-molded 50,000 times repeatedly. The surface condition remained almost the same. The surface roughness hardly changed. This shows that these dies can press-mold glass having a high melting point, such as SK-12. Accordingly, by press-molding glass by means of the dies for press-molding of this invention, it is possible to press-mold a large quantity of glass optical elements having high melting points and shapes which was difficult to attain by a grinding process. As a result, all the requirements which are necessary to directly press-mold the above-mentioned glass optical elements with high accuracy were met. It enabled press-molding a large quantity of the glass optical elements having high melting points and shapes which was impossible prior to this invention. Cemented carbide consisting mainly of WC was used as the base material of the die for press-molding in this embodiment. It goes without saying that any other material can be used to attain the same results that has heat resistance and sufficient strength to withstand the press-molding process of optical glass. However, it is preferable to use cemented carbide mainly consisting of WC, cermet mainly consisting of TiN or TiC, or WC sintered compact. As for the intermediate layer, alloy films of Ni-W-P, Ni-Cu-B (both embodiments), Cu-Ti, Si-Zr, and Ni-Mo amorphous alloy film (the latter three examples not falling within the scope of the claims of this invention) were used with cutting layers of Ni, SiC, TiN, and Ta 2 O 5 . It goes without saying that the same results can be obtained by using the alloy films shown in the embodiments 1 to 5 with cutting layers consisting of other metal, carbide, nitrogen, and oxide. As far as the protective layer is concerned, Pt-Ir was used in this embodiment, but the same results could be attained by using an alloy film of precious metal which includes at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W and Ta. Furthermore, this embodiment referred to the manufacturing process of a hollow-shaped die with 1 mm radius of curvature. Shapes which are difficult to attain with conventional grinding methods, such as dies for non-axisymmetric lenses or microprism arrays, can also be processed with this method.

Claims: A die for press-molding glass optical elements comprising: (a) a base material (13) having heat resistance and sufficient strength to withstand press-molding of optical glass elements; (b) a first alloy film (12) on said base material (13) to form a cutting layer; and (c) a surface protective layer (11) made of a second alloy film which comprises at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W, and Ta, characterized in that said first alloy film comprises P or B and one metal selected from the group consisting of Ni, Co, and Fe, and one metal selected from the group consisting of Si, Ti, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, and Ir. A die as claimed in claim 1, wherein an intermediate layer (73) comprising at least one film comprising a material selected from the group consisting of metal, carbide, nitrogen, and oxide is present between said base material and said cutting layer. A method of manufacturing a die for press-molding glass optical elements, comprising the steps of: (a) forming a base material (13) having heat resistance and sufficient strength to press-mold glass optical elements into a shape similar to a desired shape; (b) forming a film (12) comprising a first alloy film by means of at least one method selected from the group consisting of a plating method, an evaporation method, a sputtering method, and an ion plating method on top of said base material to form a cutting layer; (c) cutting said cutting layer precisely to the desired shape; and (d) forming a second alloy film (11) containing at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Os, Ru, Re, W, and Ta on top of said cutting layer, characterized in that said first alloy film comprises P or B and one metal selected from the group consisting of Ni, Co, and Fe, and one metal selected from the group consisting of Si, Ti, Cu, Zr, Nb Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, and Ir. Use of the die as claimed in claim 1 or 2 for press-molding glass optical elements at a press-molding temperature of 650°C and higher.

Inventors: INOUE KENJI, KASHIWAGI YOSHINARI, KATAOKA HIDENAO, MORIMOTO SATORU, NAKAMURA SHOJI, UMETANI MAKOTO, INOUE, KENJI, KASHIWAGI, YOSHINARI, KATAOKA, HIDENAO, MORIMOTO, SATORU, NAKAMURA, SHOJI, UMETANI, MAKOTO, INOUE, KENJI C/O MATSUSHITA ELECTRIC IND., KASHIWAGI, YOSHINARI C/O MATSUSHITA ELECTRIC IND., KATAOKA, HIDENAO C/O MATSUSHITA ELECTRIC IND., MORIMOTO, SATORU C/O MATSUSHITA ELECTRIC IND., NAKAMURA, SHOJI C/O MATSUSHITA ELECTRIC IND., UMETANI, MAKOTO C/O MATSUSHITA ELECTRIC IND.
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: C03B11
IPC codes: C23C14, C03B11, B32B15, C23C28